CN-0211 Datasheet, PDF (4/6 Pages) Analog Devices – IF Band-Pass Filter Bank Switching Network for Wireless Infrastructure

CN-0211
Circuit Note
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
105
115
125
135
145
155
165
175
FREQUENCY (MHz)
–8
–9
–10
–11
–12
–13
–14
125
130
135
140
145
150
155
FREQUENCY (MHz)
Figure 5. 140 MHz (Center Frequency) 20.7 MHz (1 dB BW) 856592 SAW Filter Frequency Response Measured on Evaluation Board with Switches
0
–9.0
–10
–9.5
–20
–10.0
–10.5
–30
–11.0
–40
–11.5
–50
–12.0
–60
–12.5
–70
–13.0
–80
–13.5
–90
–14.0
105
115
125
135
145
155
165
175
130
135
140
145
150
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 6. 140 MHz (Center Frequency) 16.18 MHz (1 dB BW) 856684 SAW Filter Frequency Response Measured on Evaluation Board with Switches
COMMON VARIATIONS
The absorptive version of the ADG904 switch can also be used
in this filter bank switching circuit. The absorptive version
contains 50 Ω shunt resistors on the RFx ports. This results in a
good 50 Ω match when the switch is in the off state. This is
important in some applications where reflected signals in the
off channels need to be absorbed.
The circuit can be easily scaled to include more or fewer filter
channels. Depending on the number of channels, other switches
from the ADG9xx family may be better to use and offer more
flexibility with layout. The ADG936 is a dual SPDT switch, the
ADG918 is an SPDT switch, and the ADG901 is an SPST
switch. All of these switches are available in both absorptive and
reflective configurations.
CIRCUIT EVALUATION AND TEST
The circuit is designed to be connected to a vector network
analyzer (VNA) via SMA type connectors. The SMA connectors
on the board are female. To switch between each filter channel
there are jumper terminals on the board that can be manually
changed. Note that one of the switch throws in each ADG904-R
switch is not used. Therefore, when these unused switches are
selected, the RF input and RF output ports are isolated, i.e., the
switches are not connected to a filter.
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